(Edit: 3 replies since I started writing. I'm too slow)
Yeah thats one of the key things with the beasts we are creating and why I'm studying specific periods and their entire biological makeup.
The game simulates the full ecosystem, so animals eat each other, plants grow*... spread etc. I'm being very careful about realistically fitting animals into the food chain. That way if you upset the food chain, and get swarmed by desperate predators.. it will be you to blame!
*I actually coded it in so each individual piece of grass grows depending on how its lit and how wet the ground is. Its an embarrassing waste of CPU. I need more self control.
with fossils allowing you to find traces and stuff,
I do want to have fossils of existing and previous forms of the creatures. This will allow you to research the creatures without having to capture/kill one, if you are being very defensive with your base.